FIG. 1 shows a configuration of a mobile communication system in the 3GPP. Illustration of nodes not related to background art and nodes not needed for explanation is omitted.
In FIG. 1, a core network 10 is a network that is mostly administered by an operator which provides a mobile communication service. In this example, EPC (Evolved Packet Core) or UMTS (Universal Mode Telecommunications System) packet switched core network is assumed.
An external network 20 is an IP (Internet Protocol) network that is connected to the core network 10 through an anchor GW 100. Examples of the external network 20 include the Internet, a corporate network and a home network. The external network 20 may be a network that is administered by the same administrator as the core network 10 in some cases.
The anchor GW (gateway) 100 is a gateway that acts as an anchor when a mobile terminal 700 moves between radio base stations or moves to a different radio access network. Further, the anchor GW 100 operates also as a gateway for connecting the core network 10 and the external network 20. Specifically, when the anchor GW 100 receives a packet addressed to the mobile terminal 700 from the external network 20, the anchor GW 100 transfers it to the mobile terminal. Although the anchor GW 100 is located within the core network 10 in FIG. 1, it may be located in the external network 20.
A policy setting node 200 has a function of setting a transfer policy for regulating packet transfer to the mobile terminal 700 to the anchor GW 100.
The authentication server 300 stores information associated with the mobile terminal 700 or its owner (subscriber) and also stores key information required to perform authentication of the mobile terminal 700. The authentication server 300 executes authentication through a mobility management node 500 when the mobile terminal 700 connects to a radio base station 600.
An access GW 400 establishes an IP packet channel between the anchor GW 100 and the access GW 400 and between the access GW 400 and the mobile terminal 700 in response to a request from the mobility management node 500. As a result, a channel through which an IP packet can be transferred is established between the anchor GW 100 and the mobile terminal 700.
The mobility management node 500 mediates authentication of the mobile terminal 700 and downloads the information associated with the mobile terminal 700 from the authentication server 300. Based on the obtained information, the mobility management node 500 requests the access GW 400 to establish a channel through which an IP packet can be transferred.
A radio access network 60 relays user data and control data between the mobile terminal 700 and the core network 10. The radio access network 60 includes the radio base station 600. The radio base station 600 has a function of connecting with the mobile terminal 700 by radio access technology.
The mobile terminal 700 has a radio interface and connects to the radio base station 600 by radio access technology. After connecting to the radio base station 600, the mobile terminal 700 can communicate with a communication node 800 by IP using a channel for IP packet transmission that is built between the anchor GW 100 and the mobile terminal 700.
Correspondences between the elements shown in FIG. 1 and the elements of the EPC of the 3GPP are as follows. The anchor GW 100 corresponds to PDN-GW (Packet Data Network Gateway). The policy setting node 200 corresponds to PCRF (Policy and Charging Rules Function). The authentication server 300 corresponds to HSS (Home Subscriber Server). The access GW 400 corresponds to S-GW (Serving Gateway). The mobility management node 500 corresponds to MME (Mobility Management Entity). The radio base station 600 corresponds to eNB (enhanced NodeB). The mobile terminal 700 corresponds to UE (User Equipment). Further, LTE (Long Term Evolution) is used for radio access technology of EUTRAN (Evolved UMTS Terrestrial Radio Access Network) connected to the EPC.
The communication node 800 is anode having a communication function using IP and is located in the external network 20. Specific examples of the communication node 800 include a PC (Personal Computer), a printer, an application server and the like. Particularly, when the external network 20 is a home network, a digital home appliance having an IP communication function such as a television, a video recorder, an audio recorder and a media server is assumed as the communication node 800.
The sequence chart of FIG. 2 shows the flow of a process when the mobile terminal 700 connects to the radio base station 600 in the 3GPP mobile communication system shown in FIG. 1. For simplification, a part of the procedure is omitted. For the exact procedure of initial connection, see clause 5.3.2 “Attach Procedure” in 3GPP TS 23.401 V9.1.0 (Non Patent Literature 1).
First, in Step S100, the mobile terminal 700 establishes a radio link for transmitting and receiving a control signal with the radio base station 600. After that, the mobile terminal 700 transmits an attach request to the mobility management node 500 (Step S101). The attach request contains identification information of the mobile terminal 700. Further, in the case of selecting the anchor GW 100 desired by the mobile terminal 700 rather than the anchor GW 100 assigned by default by the core network 10, the attach request transmitted from the mobile terminal 700 contains the identifier of the anchor GW 100. In the 3GPP, the identifier of the anchor GW 100 is called APN (Access Point Name). Although the attach request contains various other information, those information are omitted since they are not directly relevant to the explanation here. In the following explanation also, only necessary information is explained among the information contained in signals.
In Step S102, an authentication process and a communication hiding process that involve the mobile terminal 700, the radio base station 600, the mobility management node 500 and the authentication server 300 are performed. As a result, the mobile terminal 700 and the core network 10 authenticate each other, and further a control signal is hidden between the mobile terminal 700 and the mobility management node 500, and a key to ensure integrity is shared. Data and a control signal in the radio interval are hidden also between the mobile terminal 700 and the radio base station 600, and a key to ensure integrity is shared.
In Step S103, the mobility management node 500 transmits a bearer setting request to the access GW 400 in order to establish a channel between the mobile terminal 700 and the access GW 400. The signal contains the address of the anchor GW 100 and a set value for creating an appropriate channel. When the mobile terminal 700 makes an initial connection to the core network 10, the mobility management node 500 adds the address of the anchor GW 100 acquired from the authentication server 300 to the bearer setting request. After that, when the mobile terminal 700 transmits an attach request (connection setting request) that contains the identifier of the anchor GW 100, the mobility management node 500 performs address resolution of the identifier (FQDN (Fully Query Domain Name) format) of the anchor GW by DNS (Domain Name System) and stores the resolved address into the bearer setting request.
In Step S104, the access GW 400 that has received the bearer setting request transmits a path setting request to the anchor GW 100 using the address of the anchor GW 100 stored in the request.
In Step S105, the anchor GW 100 requests the policy setting node 200 to set a transfer policy when transferring an IP packet to the mobile terminal 700 by the anchor GW 100. As a result, the policy setting node 200 sets transfer policy information to the anchor GW 100.
In Step S106, the anchor GW 100 transmits a path setting response to the access GW 400 as a response to the path setting request. As a result, a channel for IP packet transfer is established between the access GW 400 and the anchor GW 100.
In Step S107, the access GW 400 transmits a bearer setting response to the mobility management node 500 as a response to the bearer setting request.
In Step S108, the mobility management node 500 transmits a path setting request for establishing a channel for transferring an IP packet between the access GW 400 and the radio base station 600 to the radio base station 600.
In Step S109, the mobility management node 500 transmits an attach completion notification to the mobile terminal 700.
In Step S110, a radio link for exchanging a data packet is set up between the radio base station 600 and the mobile terminal 700.
Finally, in Step S111, a channel (which is called EPS (Evolved Packet System) bearer in the 3GPP) for transferring an IP packet between the mobile terminal 700 and the anchor GW 100 is established. The mobile terminal 700 can thereby transmit and receive an IP packet to and from the communication node 800 in the external network 20 using the channel. Thus, communication between them becomes possible.
Note that packet filters are configured at the endpoints of the channel set up between the mobile terminal 700 and the anchor GW 100. Specifically, the channel does not let all of IP packets pass through, and packets that can pass through the channel are limited. The conditions for an IP packet to pass through the channel in the direction from the external network 20 to the mobile terminal (which is called a downlink direction) are set to the anchor GW 100 in the above Step S105. The anchor GW 100 discards an IP packet that does not meet the preset conditions for passage without transferring it in the downlink direction.
The case where the radio base station 600 is a typical macro cell base station is described above. Currently, discussions about a small-scale radio base station having a significantly smaller cell size (cover area) than the macro cell base station are actively taking place in several standardization groups related to the mobile communication system, which include the 3GPP. A cell formed by the small-scale radio base station is called a femtocell or a home cell. Further, the small-scale radio base station is called a femtocell base station or a home base station. In the 3GPP, the femtocell base station is defined as HNB (Home Node B) and HeNB (Home evolved Node B). Hereinafter, HNB and HeNB are referred to collectively as H(e)NB. The purpose of introducing the femtocell is not only to complement a dead zone. For example, one of other purposes is to make coordination between an information home appliance having a network connection function and the mobile terminal 700 by installing the femtocell base station in user's home.
FIG. 3 shows one of ideas to realize H(e)NB under study by the 3GPP. In the configuration of FIG. 3, the anchor GW 100 and the radio base station 600 are integrated in a H(e)NB 1100. In this case, although the anchor GW 100 is located not in the core network 10 but in a network of a user (home network), the interfaces between the nodes and functions are substantially the same as those of the configuration in FIG. 1.
Differences between FIG. 1 and FIG. 3 are further described. The H(e)NB 1100 creates an IPsec tunnel with a security GW 1000 located in the core network 10 and transfers communications between the anchor GW 100 or the radio base station 600 and each node located in the core network 10 using the IPsec tunnel. Further, those communications are transferred to the security GW 1000 via a broadband router 900 located in a home network 20 and through an access network 30 of a provider that provides an access service by ADSL (Asymmetric Digital Subscriber Line), FTTH (Fiber To The Home) or the like.